The proposals outlined in this application aim to extend the range of available photogenerated reagents, to increase our understanding of the labelling process, and to exploit these reagents in the solution of a number of significant biological problems. The chemical labelling of biological macromolecules has been very important in establishing the relationship between the structure and function of these molecules, and the development of highly reactive reagents generated photochemically has recently given a fresh impetus to work in this area. In the present work, the utility of existing and of new sources of carbenes and nitrenes will be explored, and the efficacy of these reactive species in labelling experiments will be investigated. We intend to look at the potential of photogenerated reagents as probes of biological membranes, to answer questions about the location and distribution of membrane proteins (e.g. in the erythrocyte and in bacteria), to discover how small molecules (e.g. amphipatic drugs) interact with membranes, and to elucidate the nature and mechanism of an oligopeptide transport system. Other studies will focus on the behavior of photogenerated spectroscopic reporter molecules in membranes and in proteins, and on the irreversible "switching" of allosteric enzymes to the liganded state. Our overall aims are (a) to provide a foundation (at present lacking) upon which the tactical design of photogenerated reagents can be based, and (b) to apply the method to a number of challenging biochemical questions.